Method of plating metals



Patented Dec. 23, 1941 METHOD or PLATING METALS Ulrich Raydt and Karl Staubwasser, Osnabruck,

Germany, assignors to Firms Osnabriicker Kupfer-und Drahtwerk, Osnabruck, Germany, a

firm of Germany No Drawing.

Application September 27, 1938,

Serial No. 231,976. In Germany May 14, 1937 3 Claims.

This invention relates to a method of plating tubes, tubular bodies, wires, rods and the like. Whereas for plating bodies of this nature recourse has hitherto generally been had to roller pressure in order successfully to effect the plating, in the method according to the present invention no rolls or the like are employed. According to the invention the bodies to be united are slipped one over the'other, a greater or less amount of clearance being left between them, and are then heated to a temperature such that'they become united the one to the other, care being taken by suitably dimensioning the parts and regulating the temperature to which they are heated and, if

necessary, by suitably selecting the metals or alloys employed, that the parts press with as great pressure as possible one against the other owing to the differences in their coefficients of expansion and do not come apart. It may also be necessary to regulate the contraction or shrinkage" by suitably cooling the parts and thereby to assist in forming the welded union.

If, for example, a tube has to be lined with a material which has a higher coeflicient of expansion than the material of the tube, the inner tube exerts a heavy pressure on the outer tube when the heating takes place. It may be necessary to provide more or less clearance between the two tubes in order that the inner tube may not be crumpled or buckled owing to its greater expansion. Too great differences in expansion can however be compensated, as already mentioned, by heating and/or cooling the individual tubes to different extents.

In order to prevent the welded union from becoming loose on cooling owing to the greater contraction of the inner tube, either the inner tube can be kept hot for a longer time, so that the contraction of the outer tube may take place in advance or the contraction of the inner tube can be prevented or limited by mechanical means, for example by introducing a metal rod or a cooled tube or the like into the inner tube.

It, on the other hand, the coefficient of expansion of the outer tube is higher than that of the inner tube it is rather diflicult to obtain the pressure necessary fopeifecting the union. In this case care must be taken from the start by drawing the tubes closely one over the other that the diameter of the inner tube is as large as possible. Further, by stronger heating of the inner tube and, if necessary, cooling of the outer tube provision mustbe made for the inner tube to exert the desired pressure on the outer tube.

It is advantageous before heating th materials to the welding temperature to draw the inner and outer tubes over one another, in order to obtain from the start as close a contact of the two tubes as possible and also to expel any air present between the tubes. It is also advisable to flange over the edges of the tube in order to exclude air from the'surfaces to be united. For. the same reason it is recommended that the material should be heated in a reducing atmosphere.

The production of faultless plating is facilitated if the thin coating of themetal to be plated is deposited on the core metal. This procedure is, however, usually not necessary.

A steel tube of for example 30 mm. internal diameter and 36 mm. external diameter is to be coated and plated with a copper tube. For this purpose a copper tube of an internal diameter of approximately 36.5 mm. and an external diameter of approximately 37 .3 mm. is preferably employed. In both cases bright drawn tubes are used. Before the plating the copper tube is degreased internally and the steel tube is degreased externally and the tubes are mechanically cleaned, for example by means of brushes. After the steel tube has a bright metallic surface on the outside it is preferably copper coated by an electrolytic meth- 06. by a short immersion in a copper bath and then rinsed at once in clean water. The dry tubes; after being cleaned in thismanner, are then treated by a known process with carbon tetrachloride or a chlorinated hydrocarbon, either by allowing the liquid to evaporate on the clean surfaces or by bringing the surfaces into contact which they are heated in a reducing atmosphereto a welding temperature of about 1000" C. The tubes are then drawn through a die disposed in front of the furnace which has a passof a diameter of about 36.7 mm., so that the reduction in diameter amounts to only a few tenths of a millimeter. After the tubes have been plated in this taken that the first pass is effected very carefully of binder metal so that said tube and core can and that an intermediate annealing is undertaken in order to prevent the plated metals from comafter the tubes have been suitably cleaned, and

pressing the inner tube against the outer tube, for example by drawing or by expanding it by means of a mandrel. The tube is then prepared for the external plating which is carried out in the manner indicated above.

The internal plating takes place first in the annealing furnace since the inner copper tube is pressed firmly against the steel tube owing to its higher coefficient of expansion.

'If other metals have to be plated the procedure is similar. c

Plating is successfully effected by the new process in spite of the views which have hitherto been held to the effect that it is not possible to unite tubes by drawing and that the plating of tubes can only be performed by rolling the tubes. The new process is considerably simpler and more economical than those hitherto known.

As has already been indicated, instead of a ,fixed or solid die, a die with rolls, rollers or balllike profiled parts can be employed in which the friction and therefore the wear is considerably less than when a fixed or solid die is employed.

Obviously wires, rods and the like as well as in some cases profiled objects can be plated in a similar manner by means of the new process.

causes the adjacent surfaces of the core and 1 tube to be pressed together, whereby the tube is When using the new plating process it is generally advisable to work in a protective atmosphere of a reducing or inert gas if the peneration of the oxygen of the air is not effectively prevented by the pressing together of the materials to be plated. The material which has been plated by the new process can be worked up further in known manner by plastic deformation either by hot or cold methods.

What we claim is: r

l. The method of plating a core of one metal in the form of a tube, wire, rod and the like with a coat of another metal comprising slipping a tube of other metal directly onto the core of the One metal without any intermediate layer integrally plated directly on said core solely by said heating and the pressure produced by differential expansion without plastically deforming either said tube or core.

2. The method of plating a core of one metal in the form of a tube, wire, rod and the like with a coat of another metal comprising slipping a tube of other metal directly onto the core of the one metal without any intermediate layer of binder metal so that said tube and core can contact each other, heating said core and tube to a temperature at which said metals will integrally unite under pressure, cooling one of said metals having too high a coeflicient of expansion to a temperature which is still sufliciently high to enable said metal to' unite with the other metal, the fit of said tube and core being so close that when said tube and core are so heated and the one or the other thereof cooled the tube is pressed against the adjacent surface of the core and integrally, directly united therewith without exerting additional mechanical pressure and without plastic deformation of either metal.

' 3. The method of plating a core of one metal in the form of a; tube, wire, rod and the like with a coat of another metal comprising slipping a tube of other metal directly onto the core of the one metal without any intermediate layer of binder metal so that said tube and core can contact each other, fianging over the ends of said tube inwardly to close said ends against admission of air, heating said core and tube to a temperature at which said metals will integrally unite under pressure, the flt of the tube on said core being so close that when heated the differential of expansion of the tube and core causes the adjacent surfaces of the coreQand tube to be pressed together, whereby the tube is integrally plated directly on said core solely by said heating and the pressure produced by differential expansion without plastically deforming either said tube or core.

ULRICH RAYDT. KARL STAUBWASSER. 

